Electro-magnet



(No Model.)

T. COCHRAN.

A ELECTRO MAGNET. No. 265,485. Patented Oct. 3, 1882.

UN ITED STATES PATENT OFFICE.

THOMAS COCHRAN, OF BROOKLYN, NEW YORK.

ELECTRO-MAGNET.

SPECIFICATION forming part of Letters Patent No. 265,485, dated October3, 1882,

Applicaiion filed September 28, 1880.

(No model.)

To all whom it may concern:

Be it known that I, THOMAS COCHRAN, a citizen of the United States,residing at Brooklyn, in the county of Kings and State of New York, haveinvented certain new and useful Improvements in Electro-Magnets; and Ido hereby declare that the following is a full, clear, and exactdescription thereof, reference being had to the accompanying drawings.

rlhe object ot' my invention is to provide an improved meansof adjustingor controlling the attractive force exerted by an electro-magnet uponits armature, so that the said force may be kept practically constant,irrespective ot' any increase in the normal strength of the inducingelectric current traversing` the helices ofthe magnet. Such a means ofadjustment is of especial value in connection with electro-magnets whichare employed in the construct-ion of telegraphic receiving-instruments,as the strength of the current at the receiving-station on longtelegraph-lines i'luctuates widely at times, especially duringunfavorable weather, and the consequent irregularity of the forceexerted upon the armature seriously interferes with the operation of theapparatus.

Heretofore the eii'ects due to the varyin g force with which thearmature is attracted, under the conditions stated, have usually beencounteracted by means of an adjustable retracting-spring attached to thearmature and acting in opposition to the force ofthe electromagnet, thetension of which spring could be varied within certain limits tocorrespond with the variations of the opposing force in theelectro-magnet.

Myinvention consists,in general,ot'amethod of' and apparatus forregulating or controlling the intensity of the eld of torce of theelectromagnet, or, in other words, the free magnetism which emanatesfrom the poles of the electro-magnet and which exerts its attractionupon the movable armature. 'Under ordinary conditions this eld of forcevaries in intensity in the same proportion that the strength of theinducing-current in the coils of the magnet varies.

My invention consists in formin g an ad j ustable magnetic connection orshunt between two points of contrary polarity in the electromag net,whereby a certain portion (more or less considerable) ot' the magnetismdeveloped by the action ot' the current may be diverted from the tieldot' force, and thus prevented from acting upon the armature. Theinvention t'urther consists in certain special apparatus and devices forthe convenient application of the principle ot' the invention topractical use.

In the accompanying drawings, Figure l is a diagram illustrative oftheprinciple of my invention. Fig. 2 is a plan view of a telegraphicreceivinginstrument to which my invention has been applied. Fig. 3 is afront elevation ofthe same, and Fig. 4C represents a modilicution oftheapparatus.

rlhe law ot' magnetic action upon which my invention is based will bebest understoodl by reference to the diagram in Fi. 1, in which Arepresents a bar ot' sot't iron bent into the 'forni of the letter U andhavingits limbs enveloped by coils or helices B B, composed of a wire,in w, wound upon the bar in many convolutions. Vhen an electric currenttraverses the coils D B the bar A becomes magnetic and exerts anattractive force upon movable bodies ot'- iron, steel, and othermagnetic metalsin its vicinity. This l'orce is ofa dual character, andis manifested principally at the ends as of the bar A, which are termedthe north and south77 magnetic poles of the bar, and it diminishesgradually from the poles to a point,m, near the middle ot' the length ofthe bar, where itis null. It a bar ot1 soft iron, D, long enough toreach from one poleto the other ot' the bar A, is placed in front ofthem at a little distance, so as to be within the range of theirattractive influence, (which is technically termed a field of force,")it will be powerfully attracted by the contrary poles a and s, and,unless held back by a superior force, will fly into contact with them.When this has taken place the bar D is said to have closed the magneticcircuit ot' the bar A, and if the mass or crosssection of the bar D isequal to or greater than that ot the bar A little or no attractive forcewill be mani` fested exterior to the bar in any portieri ouf its length.Thus it will be understood that if the contrary poles of a magnet areconnected by a bar of magnetic metal ot' a cross-section or mass notless than that of the bar itself its attrac- IOO tion for other bodiesis practically destroyed. Il", however, the mass of the connecting-baris less than that of the magnet, only a portion of the magnetic actionwill be diverted, while the remainder will manifest itself at the poles,as before. If therefore the connection is formed by laying a tapering orwedge-shaped piece of soft iron, C, across the poles of the magnet A, asseen in Fig. l, with its thin end touching one of them, the armature Dwill still continue to be attracted,but with somewhat diminished force,and if the wedge C is moved in the direction indicated by the arrow theportion of its mass between the poles a and s will constantly increase,and more and more of the magnetism in the tield of force at the polewill be diverted, and the attraction ofthe poles for the armature I)will be correspondingly weakened.

As the attractive force ofan electro-magnet, other things being equal,is always in proportion to the strength of current traversing the coils,it is obvious that any increase in the magnetic force exerted upon thearmature I) resulting from an increase in the strength of the currenttraversing the coils B B may be compensated by diverting or shunting thesurplus through the regulating-bar C, so that the action of the magnetupon its armature may be rendered practically uniform.

InFigs. 2 and 3 I have shown an application of my invention to anordinary telegraphic re ceivinginstrument, asf a relay or sounder; but Iremark that it is equally applicable to electromagnets employed for anypurpose whatever, which are subject to irregularities of actionresulting from variations in the electric current hy which they areoperated.

A is the core ofthe electro-magnet, consisting of two straightcylindrical bars of soft iron united by a yoke, the straight bars orlimbs being enveloped in coils B B in the usual mannel.

I) is the armature, mounted upon screwpoints d d, so as to move to andfro under the alternate influence of "the attractive force of the polesa and s, and of thel antagonistic retracting-spring E, in the ordinarymanner of such apparatus.

rI`he regulating-bar or magnetic shunt C is preferably made in two partsor pole-pieces, c and c', which pass through transverse slots in thecores very near the poles, as shown in Figs. 2 and 3. I prefer that thetwo parts c and c should be constructed with inclined faces overlappingeach other, as best seen in Fie'. 3, as greater delicacy of ad j ustmentmay be obtained thereby.

The adjustment of the apparatus maybe conveniently effected by means ofa spindle, Il, carrying right and left screw-threads j' and j", andturned by a milled head, F. The right and left screws work throughcorresponding nuts or projections fixed to the pole-pieces c and c,respectively. It will be readily understood that by turning the milledhead Fl the pole-pieces c and c may be made to approach toward or recedefrom each other, and that the effect will be to increase or diminish theactual mass of metal which constitutes the magnetic shunt for divertingthe magnetism from the poles n and S.

rIhe antagonistic spring' E has a constant and invariable tension, anddoes not require to be adjusted or altered. In fact, the method ofoperation in my apparatus is precisely the reverse of that ordinarilyemployed, as I regulate the varying force of the attraction upon thearmature,leaving the resistanceot'thearmature constant, instead ofvarying the resistance of the armature to correspond with the varyingdegrees of magnetic force in the electromagnet.

rIhere are many different ways in which such an apparatus may beconstructed without departing in the least from the principle of myinvention; but I have not deemed it necessary to show more than one ofthese modifications, as others will readily suggest themselves topersons skilled in the art. For example, in Fig. 4t I have shown atapering wedge of soft iron placed across the poles of theelectro-magnet, and movable to and fro by means of a slowmotion screwand milled head, G. The mode of operation is of course the same as thatalready fullyexplained in connection with Figs. l, 2, and 3.

I do not herein claim the specific mechanical devices hereinbe'foredescribed, except as they are involved in the following claim, as Icontemplate embodying the same,in so far as they are novel, in anapplication to be hereinafter tiled by me.

I claim as my invention- The combination, substantially as hereinbeforeset forth, of an electro-magnet placed in an electric circuit, anarmature, and an interposed short-circuiting bar.

In testimony whereof I have hereunto subscribed my name this 25th day ofSeptember, A. D. 1880.

THOMAS COCII RAN. I

Witnesses:

NELSON Znnnrsmn, .FRANK L. Porn.

IOO

